Wrens in Britain have a more powerful song than their cousins from eastern North America, and the call notes are different, even though they are considered the same species.
Addendum July 2010: They are now considered separate species, Eurasian and Winter Wren.
(Apr, Herts, England).
The song of the eastern US (Winter) Wren sounds weaker by comparison, with less frequency variation (July, ME).
Most Winter Wrens in the eastern United States sing only two different songs, albeit amazingly long and complicated vocalizations (western birds, now a separate species, Pacific Wren, have a larger repertoire).
time scale reduced
Alarm calls are uttered rapidly in a staccato series. The bird in the foreground was a male; the nearby bird with the doubled call was presumably the female (Apr, Herts).
Another example of the doubled call (Apr, Suffolk).
Another commonly heard call, a rapid series of notes (Apr, Herts).
The eastern US Winter Wren alarm call is usually uttered in pairs, but is quite different from the above calls (Oct, PA).
Less commonly heard, a staccato alarm by a Winter Wren (Mar, PA).
For a discussion regarding the differences in calls and songs of eastern and western US Winter Wrens, including a possible species split, see Earbirding. To my ears, the calls of British Wrens are closer to those of the western US birds.